Preheat your oven to 400°F (200°C).
Cut the baby potatoes in half. Chop the red onion and zucchini into 1-inch (2.5 cm) pieces. Slice the whole lemon into thick rounds.
Place the potatoes, onion, zucchini, and lemon slices on a large rimmed baking sheet. Drizzle with 2 tablespoons of the olive oil. Season with 1/2 teaspoon of the kosher salt and 1/4 teaspoon of the black pepper. Toss to coat and spread into an even layer.
Pat the chicken thighs dry with paper towels. Season all over with the remaining 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper.
Nestle the chicken thighs skin-side up among the vegetables on the baking sheet. Roast in the preheated oven for 20 minutes.
While the chicken roasts, whisk together the chicken broth, lemon juice, lemon zest, remaining 2 tablespoons olive oil, honey, and minced garlic in a small bowl.
Remove the baking sheet from the oven. Pour the broth mixture evenly over the vegetables and around the chicken, avoiding pouring it directly on the chicken skin.
Return the pan to the oven and roast for another 20 to 25 minutes. The chicken is done when a meat thermometer inserted into the thickest part reads 165°F (74°C) and the potatoes are fork-tender.
Garnish with chopped fresh parsley before serving.